Phase modulated data link for low-swing wireline applications

ABSTRACT

A communication system comprises a transmitter and a receiver that communicate differential phase modulated data over a wireline channel pair. The transmitter encodes data symbols by generating first and second data signals with differentially phase shifted signal transitions with respect to one another. The receiver receives the first data signal and the second data signal and samples the first data signal based on a signal transition timing of the second data signal to generate a first output data symbol. The receiver furthermore samples the second data signal based on signal transition timing of the first data signal to generate a second output data symbol.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/864,079 filed on Apr. 30, 2020, which claims the benefit of U.S.Provisional Application No. 62/848,550 filed on May 15, 2019, each ofwhich is hereby incorporated by reference in its entirety.

BACKGROUND

Power in digital logic circuits is strongly related to f·C·V² where f isthe frequency of the signal, C is the capacitance of the circuit, and Vis the voltage of the signal. Therefore, reducing the voltage swing ofthe signal can significantly reduce power consumption. However, lowvoltage signals using traditional voltage-level signaling are subject toerrors caused by voltage noise.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the embodiments herein can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings.

FIG. 1 is a circuit diagram illustrating a first example embodiment of acommunication system using a phase-modulated data link.

FIG. 2 is a waveform diagram illustrating an example embodiment of asignaling scheme for a phase-modulated data link.

FIG. 3 is a circuit diagram illustrating a second example embodiment ofa communication system using a phase-modulated data link.

FIG. 4A is a circuit diagram illustrating a first example embodiment ofan amplifier for a receiver of a communication system using aphase-modulated data link.

FIG. 4B is a circuit diagram illustrating a second example embodiment ofan amplifier for a receiver of a communication system using aphase-modulated data link.

FIG. 4C is a circuit diagram illustrating a third example embodiment ofan amplifier for a receiver of a communication system using aphase-modulated data link.

FIG. 5 is a circuit diagram illustrating an example embodiment of alogic circuit for a receiver of a communication system using aphase-modulated data link.

DETAILED DESCRIPTION OF EMBODIMENTS

A communication system comprises a transmitter and a receiver thatcommunicate differential phase modulated data over a wireline link. Thetransmitter encodes data symbols by generating first and second datasignals with signal transitions that are differentially phase shiftedwith respect to one another. For example, to encode a first symbol type,the transmitter outputs a phase-shifted signal transition of a sourcesignal (e.g., a clock signal) as the first data signal and outputs anunshifted signal transition of the source signal as the second datasignal. To encode a second symbol type, the transmitter instead outputsa phase-shifted signal transition of a source signal (e.g., a clocksignal) as the second data signal and outputs an unshifted signaltransition of the source signal as the first data signal. The receiverreceives the first data signal and the second data signal and samplesthe first data signal based on a signal transition timing of the seconddata signal to generate a first output data symbol. Therefore, when thesignal transition of the first data signal leads the signal transitionof the second data signal (i.e., encoding a first symbol type), thefirst data signal will be sampled after its signal transition, therebyproducing a sample corresponding to first output symbol type.Alternatively, when the signal transition of the first data signal lagsthe signal transition of the second data signal (i.e., encoding a secondsymbol type), the first data signal will be sampled before its signaltransition, thereby producing a sample having a second output symboltype. The receiver furthermore samples the second data signal based onsignal transition timing of the first data signal to generate a secondoutput data symbol that is complementary to the first output datasymbol.

FIG. 1 is a circuit diagram of a communication system 100 thatcommunicates data using a phase-modulated data link. The communicationsystem 100 comprises a transmitter 120 and a receiver 140 thatcommunicate over a wireline channel pair including a first wire 134 anda second wire 136. The transmitter 120 receives input data signal 132and encodes the input data signal 132 as differential phase-modulatedsignals including a first data signal (e.g., Txp) on the first wire 134and a second data signal (Txn) on the second wire 136 that aredifferential in phase. The receiver 140 receives the differentialphase-modulated signals Txp, Txn and decodes the differentialphase-modulated signals Txp, Txn to generate an output data signal 152.Presuming no symbol errors occur during transmission, the output datasignal 152 will recover the symbols of the input data signal 132.

The input data signal 132 and the output data signal 152 may be encodedusing voltage levels to represent different symbol types (e.g., usingCMOS or TTL signaling). In contrast, the differential phase-modulatedsignals Txp, Txn transmitted over the wires 134, 136 instead encode thedifferent symbol types as phase differences between signal transitions(e.g., pulses) of the Txp signal on the first wire 136 and Txn on thesecond wire 134. For example, in binary phase modulation, thetransmitter 120 causes a signal transition of the Txp signal to lead asignal transition of the Txn signal (e.g., a positive phasedifferential) during a symbol period to encode a first symbol type(e.g., a first logic value), and causes a signal transition of the Txnsignal to lead a signal transition of the Txp signal (i.e., a negativephase differential) during a symbol period to encode a second symboltype (e.g., a second logic value). In one embodiment, a first symboltype is encoded by Txp leading Txn by 90 degrees and a second symboltype is encoded by Txp lagging Txn by 90 degrees. In alternativeembodiments, the transmitter 120 may apply different phase differentials(e.g., −30°, −45°, −60°, −90°, +30°, +45°, +60°, +90°, etc.) todistinguish between different symbol types. Furthermore, in someembodiments, the transmitter 120 may encode multiple binary symbols in asingle symbol period by selecting between 4, 8, or a different number ofpossible phase differentials each representing multiple bits of data ofthe input data signal 132.

The differential phase-modulated signals Txp, Txn may comprise lowvoltage swing signals that operate at substantially lower voltage swingthan the voltage swing levels encoding the input data 132. Furthermore,the wires 134, 136 may be terminated or unterminated links. In anembodiment, DC blocking capacitors may be integrated in series with thewires 134, 136.

The transmitter 120 comprises a clock generator 122, a pair ofmultiplexers 124, 126, and a pair of amplifiers 128, 130. In anembodiment, the transmitter 120 is embodied on an integrated circuit(IC) chip and is used to transmit signals to another IC chip. The clockgenerator 122 generates a first clock signal and a second clock signalthat are differential in phase. For example, the first clock signal maycomprise an in-phase clock signal Φ₀ and the second clock signal maycomprise a quadrature-phase clock signal Φ₉₀ that is phase-shifted 90°relative to the in-phase clock signal Φ₀. The first clock signal and thesecond clock signal are each provided as inputs to the multiplexers 124,126. The multiplexers 124, 126 each select between the first clocksignal and the second clock signal based on the symbol type of the inputdata signal 132. Here, a first multiplexer 124 selects the in-phaseclock signal Φ₀ in response to the data signal 132 having a first symboltype and selects the quadrature phase clock signal Φ₉₀ in response tothe data signal 132 having a second symbol type. The second multiplexer126 inversely selects the in-phase clock signal Φ₀ in response to thedata signal 132 having the second symbol type and selects the quadraturephase clock signal Φ₉₀ in response to the data signal 132 having thefirst symbol type. Thus, the multiplexers 124, 126 respectively selectopposite ones of the in-phase clock signal Φ₀ and the quadrature phaseclock signal Φ₉₀ at each symbol period of the input data signal 132.

The amplifiers 128, 130 amplify the multiplexer output signals from therespective multiplexers 124, 126 to generate the differentialphase-modulated signals Txp, Txn for transmission on the respectivewires 134, 136. In an embodiment, the amplifiers 128, 130 may generatethe phase differential phase-modulated signals Txp, Txn as low voltageswing signals. As a result, a first symbol type of the input data signal132 for a given symbol time interval is encoded by a phase shiftedsignal transition in first data signal Txp and a second symbol type ofthe input data signal 132 is encoded by a phase shifted signaltransition in the second data signal Txn.

The receiver 140 comprises a pair of input ports 162, 164, a pair ofamplifiers 142, 144, a pair of samplers 146, 148, and a logic circuit150. In an embodiment, the receiver 140 may be embodied as a circuit onan integrated circuit chip to receive a signal transmitted by another ICchip. The input ports 162, 164 receive the differential phase-modulatedsignals Txp, Txn from the wires 134, 136. The amplifiers 142, 144generate respective amplified signals based on the differentialphase-modulated signals Txp, Txn (e.g., a first amplified signalcorresponding to Txp and a second amplified signal corresponding toTxn). The first sampler 146 samples the first amplified signal based onsignal transition timing of the second amplified signal (e.g., on therising edge the second amplified signal) to generate a first sampledoutput signal A. The second sampler 148 samples the second amplifiedsignal based on signal transition timing of the first amplified signal(e.g., on the rising edge of the first amplified signal) to generate asecond sampled output signal B. Thus, if a signal transition of thefirst amplified signal leads a signal transition of the second amplifiedsignal (i.e., encoding a first symbol type), the first sampler 146 willsample a voltage of the first amplified data signal corresponding to thefirst symbol type while the second sampler 146 will sample a voltage ofthe second amplified data signal corresponding to the second symboltype. On the other hand, if a signal transition of the first amplifieddata signal lags the signal transition of the second amplified datasignal (i.e., encoding a second symbol type), the first sampler 146 willsample a voltage of the first amplified data signal corresponding to thesecond symbol type while the second sampler 148 will sample a voltage ofthe second amplified data signal corresponding to the first symbol type.As a result, the first sampled output signal A and the second sampledoutput signal B are differential in voltage such that when sampledoutput signal B has a logic high voltage level, sampled output signal Ahas a logic low voltage level, and vice versa. The logic circuit 150detects the voltage difference between the first sampler output from thefirst sampler 148 and the second sampler output from the second sampler146 and generates the output data signal 152. For example, the outputdata signal 152 may have a first logic level corresponding to the firstsymbol type when A−B is positive and may have a second logic levelcorresponding to the second symbol type when A−B is negative. Thus, thereceiver 140 demodulates the differential phase-modulated signals Txp,Txn to generate a differential voltage output. In an embodiment, thelogic circuit 150 may furthermore include digital logic to detect faultconditions (e.g., when A=B).

In an embodiment, an integrated circuit chip may comprise a transceiverthat includes both a transmitter 120 and a receiver 140. In thisembodiment, the transceiver may communicate with another transceiverchip using a bidirectional link in which each transmitter/receiver paircommunicate over a shared pair of wires. Alternatively, the transceivermay communicate with another transceiver chip using unidirectional linksin which each transmitter/receiver pair communicate over separatededicated wireline differential channels.

FIG. 2 illustrates example waveforms for encoding a binary input symbolas differential phase-modulated signals Txp, Txn. To encode a firstsymbol type (e.g., ‘1’), the transmitter 120 generates differentialphase-modulated signals Txp, Txn in which a signal transition of thefirst data signal Txp is phase shifted relative to a signal transitionof the second signal Txn during a given symbol period (e.g., Txp leadsTxn). To encode a second symbol type (e.g., ‘0’), the transmitter 120generates a differential phase-modulated signals Txp, Txn in which asignal transition of the second data signal Txn is phase shiftedrelative to the signal transition of the first data signal Txp duringthe given symbol period (e.g., Txn leads Txp).

FIG. 3 illustrates an embodiment of a communication system 300 thatcommunicates data using a phase-modulated data link. The communicationsystem 300 includes a transmitter 120 and wires 134, 136 as describedabove, and includes a receiver 340 that performs decision feedbackequalization. The decision feedback equalization compensates forfrequency dependent attenuation caused by the wires 134, 136 that maydistort the received differential phase-modulated signals Txp, Txn.Particularly, the receiver 340 applies different sample timing to thereceived differential phase-modulated signals Txp, Txn selectedaccording to a prior decoded symbol. Thus, for example, the receiver 340generates output symbols based on a first sample timing when the priordecoded symbol is a first symbol type, and generates output symbolsbased on a second sample timing when the prior decided symbol is asecond symbol type.

The receiver 340 comprises a pair of input ports, 362, 364, a pair ofamplifiers 342, 344, a plurality of samplers 354, 356, 358, 360,multiplexers 372, 374, digital logic 376, and a plurality of delayelements 346, 348, 350, 352. The input ports 362, 364 receive thedifferential phase-modulated signals Txp, Txn from the wires 134, 136.The amplifiers 342, 344 generate respective amplified signals based onthe differential phase-modulated signals Txp, Txn (e.g., a firstamplified signal corresponding to Txp and a second amplified signalcorresponding to Txn). The first and second samplers 354, 356 eachsample the first amplified signal (based on Txp) from the firstamplifier 342 based on the second amplified signal from the secondamplifier 344 (based on Txn), but each perform the sampling according todifferent timings. Particularly, the first sampler 354 samples the firstamplified signal based on timing of a signal transition in a delayedsecond amplified signal (delayed by delay element 350) while the secondsampler 356 samples a delayed first amplified signal (delayed by delayelement 346) based on timing of a signal transition in the secondamplified signal. Thus, sampling of the first amplified signal using thefirst sampler 354 occurs relatively later in the symbol period (due tothe sampling time being delayed), while sampling of the first amplifiedsignal using the second sampler 356 occurs relatively earlier in thesymbol period (due to the first amplified signal being delayed). Thefirst multiplexer 372 selects between the first sampled output from thefirst sampler 354 and the second sampled output from the second sampler356 based on a prior decided symbol. For example, if the prior decidedsymbol had a first symbol type (e.g., ‘0’), the first multiplexer 372selects the output of the first sampler 354 (sampled later in the symbolperiod), while if the prior decided symbol had a second symbol type(e.g., ‘1’), the first multiplexer 372 selects the output of the secondsampler 356 (sampled earlier in the symbol period).

The third and fourth samplers 358, 360 each sample the second amplifiedsignal based on the first amplified signal, but perform the samplingaccording to different timings. Here, the third sampler 358 samples thesecond amplified signal based on timing of a signal transition in adelayed first amplified signal (e.g., delayed by delay element 352)while the fourth sampler 360 samples a delayed second amplified signal(e.g., delayed by delay element 348) based on timing of a signaltransition in the first amplified signal. Thus, sampling of the secondamplified signal using the third sampler 358 occurs relatively later inthe symbol period (due to the sampling time being delayed), whilesampling of the second amplified signal using the fourth sampler 360occurs relatively earlier in the symbol period (due to the secondamplified signal being delayed). The second multiplexer 374 selectsbetween the third sampled output from the third sampler 358 and thefourth sampled output from the fourth sampler 360 based on a priorsymbol decision. For example, if the prior decided symbol has a firstsymbol type (e.g., ‘0’), the second multiplexer 374 selects the outputof the third sampler 358 (sampled later in the symbol period), while ifthe prior decision has a second symbol type (e.g., ‘1’), the secondmultiplexer 374 selects the output of the fourth sampler 360 (sampledearlier in the symbol period).

In an embodiment, although delay elements 348 and 350 are shownseparately, these may comprise a single delay element that outputs toboth sampler 354 and sampler 358 in an embodiment. Similarly, althoughdelay elements 346 and 352 are shown separately, in an embodiment, thesemay comprise a single delay element that outputs to both sampler 356 and360.

In an alternative embodiment, delay elements 346 and 348 may be omitted.In this case, the second sampler 356 receives the first amplified signaldirectly (i.e., un-delayed) and the third sampler 358 receives thesecond amplified signal directly (i.e., un-delayed).

The logic circuit 366 receives the respective symbol decisions from themultiplexers 372, 374 and generates the output data signal 368 based ona voltage difference between the first decided signal A from the firstmultiplexer 372 and the second decided signal B from the secondmultiplexer 374. For example, in an embodiment, the output data signal368 may be based on a voltage difference between the first decidedsignal A and the second decided signal B (i.e., A-B). Furthermore, in anembodiment, the logic circuit 366 may direct and output error conditions(e.g., A=B).

FIGS. 4A-4C illustrate examples of amplifier circuits that can be usedas amplifiers 142, 144, 342, 344 in the embodiments above. FIG. 4Aillustrates a first example embodiment of an amplifier comprising abuffer 402 and an injection-locked oscillator (ILO) 404. The buffer 402buffers an input signal to generate a buffered input signal provided tothe ILO 404. The ILO 404 generates a rail-to-rail signal based on thebuffered input signal with very low phase noise, thereby preserving thephase-modulated encoding. In operation a full voltage swing signalproduced by the ILO 404 is shifted in phase based on the received signalwhich may be of lower amplitude than the full voltage swing of the ILO404.

FIG. 4B illustrates a second example embodiment of an amplifiercomprising a linear including a buffer 406 in parallel with a variableamplifier 408 and capacitor 410. This amplifier performs linearequalization on the input signal.

FIG. 4C illustrates a third example embodiment of an amplifiercomprising an amplifier having a capacitor 412, a resistor 418, a firstinverter 414, and a second inverter 416. The capacitor 412 and theresistor 418 are configured as a low pass filter to pass high frequencysignal through the first inverter 414. In this embodiment, the amplifiermay be linear or non-linear.

FIG. 5 illustrates another example of a receiver 500. The receiver 500receives the differential phase-modulated signals Txp, Txn and generatesde-serialized 4-bit data words on a 4-bit output data channel 530. Thereceiver 500 includes amplifiers 542, 544, samplers 546, 548, a logiccircuit 502, an AND gate 504, an ILO 506, a divider circuit 508, and ade-serializer circuit 510. The logic circuit 500 furthermore optionallyincludes a reference loop 520 including a phase detector and loop filter522 and an ILO 524.

The amplifiers 542, 544, samplers 546, 548, and logic 502 operatesimilarly to the amplifiers 142, 144, samplers 146, 148, and logic 102described above in FIG. 1. Particularly, the amplifiers generateamplified signals 552, 554. The amplified signal 552 is sampled by thesampler 146 based on timing of the amplified signal 554, and theamplified signal 554 is sampled by the sampler 148 based on the timingof the amplified signal 552 to generate sampled signals A, B. The logic502 outputs a recovered data stream based on a difference between thesampled signals A, B.

The AND gate 504, ILO 506, and optional reference loop 520 collectivelyoperate to recover a clock signal from the amplified signals 552, 554.Clock recovery is performed by detecting the data period in theamplified signals 552, 554 generating an oscillating signal having afrequency based on the data period. Specifically, the AND gate generatesa signal transition on the later of the signal transitions of theamplified signals 552, 554 (e.g., when both logic signals are logichigh). Thus, the signal transition is generated once per symbol period.The ILO 506 generates a clock signal that locks to the frequency of thesignal transitions generated by the AND gate 504. The clock divider 508divides the clock signal to generate a divided clock signal (e.g., at ¼the frequency of clock signal).

The de-serializer circuit 510 includes a set of serial flip flops 512(e.g., four serial flip flops) that operate as a shift register to shiftin a symbol from the data recovery logic 502 on each clock cycle. Thus,at any given time, the set of symbols in these flip flops 512 representthe most recent set of recovered data symbols. These last four datasymbols are outputted to a set of parallel flip flops 514 (e.g., fourparallel flip flops) that output in parallel to the output data channel530 based on the divided clock signal.

The optional reference loop 520 generates an ILO control signal 526 tocontrol a base frequency of the ILO 506. While the ILO 506 can operatefree running without any control signal 526, the use of a control signal526 that sets the ILO 506 close to the expected frequency of theincoming data signal enables the ILO 506 to lock onto to frequency ofthe data signals and recover the clock signal more quickly. In anembodiment, the reference loop 520 comprises a phase detector and loopfilter 522 and an ILO 524. The ILO 524 has an injection input that isgrounded and outputs an oscillating signal based on the control signal526. The oscillating signal from the ILO 524 is provided as a feedbacksignal to the phase detector and loop filter 522. The phase detector andloop filter 522 compares the feedback signal to a reference frequencyf_(ref) and adjusts the control signal 526 in a feedback loop to matchthe output frequency of the ILO 524 to the reference frequency f_(ref)By using a reference frequency f_(ref) similar to the frequency of thedata signal, the ILO 506 can quickly lock to the clock frequency forclock recovery.

In an embodiment, where the amplifiers 542, 544 are implemented usingILOs 404 (e.g., as in FIG. 4A), the control signal 526 can also providea control signal 526 to these ILOs 404 to enable the ILOs 404 to morequickly lock to the frequencies of the respective data signals Txp, Txn.

Upon reading this disclosure, those of ordinary skill in the art willappreciate still alternative structural and functional designs andprocesses for the described embodiments, through the disclosedprinciples of the present disclosure. Thus, while particular embodimentsand applications of the present disclosure have been illustrated anddescribed, it is to be understood that the disclosure is not limited tothe precise construction and components disclosed herein. Variousmodifications, changes and variations which will be apparent to thoseskilled in the art may be made in the arrangement, operation and detailsof the method and apparatus of the present disclosure herein withoutdeparting from the scope of the disclosure as defined in the appendedclaims.

What is claimed is:
 1. A chip comprising: a set of input nodes toreceive respective first and second data signals that representdifferential phase modulated data such that, for a symbol time interval,a phase shifted signal transition in the first data signal is used toencode a first binary symbol type and a phase shifted signal transitionin the second data signal is used to encode a second binary symbol type;and a logic circuit configured to output an output signal based on adifference between the first data signal and the second data signal,wherein the output signal corresponds to the first binary symbol typeresponsive to the difference being a positive value and the outputsignal corresponds to the second binary symbol type responsive to thedifference being a negative value.
 2. The chip of claim 1, wherein thephase shifted signal transition in the first data signal has a phasedifference relative to a signal transition in the second data signal toencode the first binary symbol type, and wherein the phase shiftedsignal transition in the second data signal has the phase differencerelative to a signal transition in the first data signal to encode thesecond binary symbol type.
 3. The chip of claim 1, further comprising: afirst amplifier circuit comprising a first injection-locked oscillator,the first amplifier circuit to amplify first data signal prior to asampler circuit sampling the first data signal; and a second amplifiercircuit comprising a second injection-locked oscillator, the secondamplifier circuit to amplify the second data signal prior to the samplercircuit sampling the second data signal.
 4. The chip of claim 1, furthercomprising: a first linear gain amplifier circuit, the first linear gainamplifier circuit to amplify first data signal prior to a samplercircuit sampling the first data signal; and a second linear gainamplifier circuit, the second linear gain amplifier circuit to amplifythe second data signal prior to the sampler circuit sampling the seconddata signal.
 5. The chip of claim 1, wherein the logic circuit isfurther configured to generate a carrier clock having a carrier clockfrequency that matches a signal symbol rate of the first and second datasignals, and to deserialize the first and second output data signalsbased on the carrier clock frequency.
 6. The chip of claim 5, whereinthe logic circuit comprises: a reference loop circuit to generate acontrol signal for a first oscillator based on a difference between areference frequency signal and an oscillating signal outputted from thefirst oscillator; and a second oscillator to generate the carrier clockbased on the control signal and to adjust the carrier clock based ontransition frequency of the first and second data signals.
 7. The chipof claim 1, wherein the set of input nodes are coupled to receive thefirst data signal and the second data signal through a capacitor.
 8. Thechip of claim 1, wherein the logic circuit is further configured torecover a non-return-to-zero data stream based on samples of the firstdata signal and the second data signal.
 9. The chip of claim 1, furthercomprising: a transmitter to encode an input data signal usingdifferential phase delay modulation for transmission to another chip.10. The chip of claim 9, wherein the transmitter comprises: a clockgenerator circuit to generate an in-phase clock signal and aphase-delayed clock signal having a fixed phase delay relative to thein-phase clock signal; a first multiplexer to select the in-phase clocksignal responsive to an input data symbol of the input data signal beingthe first binary symbol type and to select the phase-delayed clocksignal responsive to the input data symbol of the input data signalbeing the second binary symbol type to generate a first transmit signal;a second multiplexer to select the in-phase clock signal responsive tothe input data symbol of the input data signal being the second binarysymbol type and to select the phase-delayed clock signal responsive tothe input data symbol of the input data signal being the first binarysymbol type to generate a second transmit signal; a first transmitbuffer to transmit the first transmit signal; and a second transmitbuffer to transmit the second transmit signal.
 11. The chip of claim 1,further comprising: a sampler circuit to sample the differential phasemodulated data, the sampler circuit to sample the first data signalresponsive to a signal transition timing derived from the second datasignal to generate a first output data sample, and sample the seconddata signal in response to a signal transition timing derived from thefirst data signal to generate a second output data sample.
 12. The chipof claim 11, wherein the sampler circuit comprises: a decision feedbackequalization circuit to equalize the first output data sample and thesecond output data sample based on one or more prior received datasymbols, the decision feedback equalization circuit comprising: a firstdelay element to delay the first data signal to generate a delayed firstdata signal; a second delay element to delay the second data signal togenerate a delayed second data signal; a first sampler to sample thefirst data signal in response to a signal transition in the delayedsecond data signal to generate a first candidate data sample; a secondsampling circuit to sample the delayed first data signal based on asignal transition in the second data signal to generate a secondcandidate data sample; a first multiplexer to select between the firstoutput data sample and the second output data based on a prior decidedsymbol to generate the first output data sample; a third sampler tosample the second data signal in response to a signal transition in thedelayed first data signal to generate a third candidate data sample; afourth sampler to sample the delayed second data signal in response to asignal transition in the first data signal to generate a fourthcandidate data sample; and a second multiplexer to select between thethird candidate data sample and the fourth candidate data sample basedon the prior decided symbol to generate the second output data sample.13. A method comprising: receiving, by a set of input nodes, respectivefirst and second data signals that represent differential phasemodulated data such that, for a symbol time interval, a phase shiftedsignal transition in the first data signal is used to encode a firstbinary symbol type and a phase shifted signal transition in the seconddata signal is used to encode a second binary symbol type; andoutputting, by a logic circuit, an output signal based on a differencebetween the first data signal and the second data signal, wherein theoutput signal corresponds to the first binary symbol type responsive tothe difference being a positive value and the output signal correspondsto the second binary symbol type responsive to the difference being anegative value.
 14. The method of claim 13, wherein the phase shiftedsignal transition in the first data signal has a phase differencerelative to a signal transition in the second data signal to encode thefirst binary symbol type, and wherein the phase shifted signaltransition in the second data signal has the phase difference relativeto a signal transition in the first data signal to encode the secondbinary symbol type.
 15. The method of claim 13, further comprising:amplifying, by a first amplifier circuit, the first data signal prior toa sampler circuit sampling the first data signal; and amplifying, by asecond amplifier circuit, the second data signal prior to the samplercircuit sampling the second data signal.
 16. The method of claim 13,further comprising: generating, by the logic circuit, a carrier clockhaving a carrier clock frequency that matches a signal symbol rate ofthe first and second data signals; and deserializing, by the logiccircuit, the first and second output data signals based on the carrierclock frequency.
 17. The method of claim 16, further comprising:generating, by a reference loop, a control signal for a first oscillatorbased on a difference between a reference frequency signal and anoscillating signal outputted from the first oscillator; and generating,by a second oscillator, the carrier clock based on the control signal;adjusting, by the second oscillator, the carrier clock based on atransition frequency of the first and second data signals.
 18. Themethod of claim 13, further comprising: recovering, by the logiccircuit, a non-return-to-zero data stream from a first output datasample sampled from the first data signal and a second output datasample sampled from the second data signal.
 19. The method of claim 13further comprising: generating, by a clock generator circuit, anin-phase clock signal and a phase-delayed clock signal having a fixedphase delay relative to the in-phase clock signal; selecting, by a firstmultiplexer, the in-phase clock signal responsive to an input datasymbol of an input data signal being the first binary symbol type;selecting, by the first multiplexer, the phase-delayed clock signalresponsive to the input data symbol of the input data signal being thesecond binary symbol type to generate a first transmit signal;selecting, by a second multiplexer, the in-phase clock signal responsiveto the input data symbol of the input data signal being the secondbinary symbol type; selecting, by the second multiplexer, thephase-delayed clock signal responsive to the input data symbol of theinput data signal being the first binary symbol type to generate asecond transmit signal; transmitting, by a first transmit buffer thefirst transmit signal; and transmitting, by a second transmit buffer,the second transmit signal.
 20. A communication system comprising: atransmitter circuit to phase modulate an input data symbol to generate afirst data signal and a second data signal that are differential inphase, where the input data symbol is encoded based on a phasedifference between the first and second data signals, and to transmitthe first data signal and the second data signal over a wired link; anda receiver circuit to receive the first data signal and the second datasignal over the wired link and output an output signal based on adifference between the first data signal and the second data signal,wherein the output signal corresponds to a first binary symbol typeresponsive to the difference being a positive value and the outputsignal corresponds to a second binary symbol type responsive to thedifference being a negative value.